I'd be... The loyal, conflicted demon who, in the end, maybe does something to help their comrade, because only by paying with their life to their cause, can they be free to give a glimmer of hope to their friend. Tragedy, blood, and tears. But also hope. Hey, if you're the one double crossing, you can't be the one to die until you've achieved your objective. Or, until you're certain that it will come to pass.

Unless the plot involves four main characters, with each of us playing two, then yes. If it's just one character each, then side characters, etc, will be thrown in. They will even exist if we are both playing two characters each.

A human or a demon. If I was only playing one character that wasn't a demon, I'd play the human, loathes demons, but as a result of being saved by one, slowly grows close to said demon, aiding them in their goal.